The invention relates to a modular converter cabinet system of a converter comprising at least one phase module having an upper and a lower converter valve, wherein each converter valve has at least two converter cells and a branch inductor, which are electrically connected in series.
Such a converter, which is also referred to as a Modular Multilevel Converter (M2LC), is known from DE 101 03 031 A1. An equivalent circuit diagram of such a three-phase converter is shown in greater detail in FIG. 1 wherein P is a positive voltage terminal of an applied DC voltage connected to a positive bus bar P0 and N is a negative voltage terminal of an applied DC voltage connected to a negative bus bar N0.
In accordance with this equivalent circuit diagram, this converter has three phase modules 1, 3 and 5, which each have an upper and a lower converter valve T1, T2 or T3, T4 or T5, T6 and each have a branch inductor LT1, LT2 or LT3, LT4 or LT5, LT6. Each converter valve T1, . . . , T6 of these phase modules 1, 3 and 5 has at least two converter cells 2, which are electrically connected in series. In the equivalent circuit diagram shown each converter valve T1, . . . , T6 has four such converter cells 2. The equivalent circuit diagram of a converter cell 2 of the M2LC is shown in greater detail in FIG. 2. Each branch inductor LT1, . . . , LT6 is electrically connected in series with the series circuit of a number of converter cells 2 of a converter valve T1, . . . , T6. By means of these converter cells 2 of the converter valves T1, T2 or T3, T4 or T5, T6 of each phase module 1 or 3 or 5 of the M2LC a stepped output voltage is generated at each output L1 or L2 or L3 of each phase module 1 or 3 or 5. The more converter cells 2 are used per converter valve T1, . . . , T6, the smoother is the output voltage at output L1 or L2 or L3. The smoother these output voltages are the lower is the outlay for an output filter.
The layout of a converter cell 2, for which the equivalent circuit diagram is shown in greater detail in FIG. 2, is likewise known from DE 10 103 031 A1. A so-called two pole subsystem 4 is provided as the converter cell 2, having two disconnectable semiconductors T11 and T12, two diodes D11 and D12 and a storage capacitor CSM. The two disconnectable semiconductors T11 and T12, especially Insulated Gate Bipolar Transistors (IGBTs), are electrically connected in series. This series circuit is electrically connected in parallel with the storage capacitor CSM. Each diode D11 or D12 is electrically connected antiparallel with a disconnectable semiconductor T11 or T12. This means that these diodes D11 and D12 are also referred to as freewheeling diodes. A terminal X2 of the converter cell 2 is formed by the connection point of the two disconnectable semiconductors T11 and T12 of the two-pole subsystem 2, while a further terminal X1 of the converter cell 2 is formed by the negative pole of the storage, capacitor CSM, which is connected electrically-conductively with an anode terminal of the diode D12 and an emitter terminal of the disconnectable semiconductor T12. A cell voltage VX21 is present at these terminals X2 and X1 of the converter cell 2. At the storage capacitor CSM, especially an electrolytic capacitor, a capacitor voltage VSM is present. The amplitude of the cell voltage VX21, depending on the switching state of the two disconnectable semiconductors T11 and T12 can be equal to the amplitude of the capacitor voltage VSM or can amount to 0V. Further details of the converter in accordance with FIG. 1 and the converter cell 2 in accordance with FIG. 2 can be found in DE 10 103 031 A1.
FIG. 3 shows an equivalent circuit diagram of a so-called double submodule 6, which can likewise be used as a converter cell 2. Such a double submodule 6 is known from DE 10 2005 041 087 A1. This double submodule 6, in accordance with the equivalent circuit diagram, has four disconnectable semiconductors T11, T12, T21 and T22, especially IGBTs, four diodes D11, D12, D21 and D22, and two storage capacitors CSM. An electronic module of the double submodule 6 shown in DE 10 2005 041 087 A1 is not shown explicitly here. These four disconnectable semiconductors T11, T12, T21 and T22 are electrically connected in series. Each of these disconnectable semiconductors T11, T12, T21 and T22 has a diode D11, D12, D21 and D22 connected electrically antiparallel to it. A storage capacitor CSM is connected electrically in parallel in each case to two disconnectable semiconductors T11, T12 or T21, T22 each electrically connected in series. These two storage capacitors CSM, especially electrolytic capacitors, are additionally electrically connected in series. The terminal X2 of the converter cell 2 is formed by the connection point of the two disconnectable semiconductors T11 and T12 and the terminal X1 of the converter cell 2 is formed by the connection point of the two disconnectable semiconductors T21 and T22. A cell voltage VX21 is present at these two terminals X2 and X1, which by comparison with the embodiment of the converter cell 2 in accordance with FIG. 2, has four potential stages. Further details of this double submodule 6 are to be found in DE 102005041087 A1.
Since the converter depicted in FIG. 1 has a plurality of converter cells 2 in accordance with FIGS. 2 and 3, this converter belongs to the so-called cell converters. The cell converters also include the cell converter “ROBICON Perfect Harmony” made by Siemens, which is described in more detail in the Siemens brochure entitled “Der Umrichter für höchste Anforderungen” (The converter for the highest requirements) with the order number E20001-A10-P590 and the publication date March 2008. This known cell converter has an intermediate voltage circuit converter as its converter cell, which generates a single-phase alternating voltage from the three phase alternating voltage. To this end each intermediate voltage circuit converter on the supply side has a six-pulse diode bridge and on the load side has a four-pulse IGBT bridge. Both bridge circuits are connected to one another electrically-conductively on the DC voltage side by means of an intermediate circuit capacitor. Each phase of this cell converter has four converter cells which are electrically connected in series on the load side. Each converter cell is linked on the supply side to a three-phase secondary winding system of a mains converter transformer. In other words, the cell converter described in the said Siemens brochure has a converter transformer with twelve three-phase secondary winding systems. If six converter cells are used for each phase of the cell converter, a converter transformer with eighteen three-phase secondary winding system is already needed. The three phases of this cell converter are connected in a star configuration, to the free ends (phase terminals) of which a load, for example an AC motor, can be connected. On page 10 of this brochure a valve cabinet with 12 converter cells is shown in the left-hand picture in the center, wherein converter cells of one phase are arranged alongside one another at a valve level of the valve cabinet. Since this cell converter has three phases, three valve levels, which are arranged spaced-apart above one another, are provided in the valve cabinet. Each valve level accommodates the converter cells of one phase, wherein these are arranged next to one another within a valve level. An inductor cabinet, in which the converter transformer is accommodated, can also be seen in this picture.
A further embodiment of the cell converter of the Siemens brochure is known from EP 1 920 528 B1 which, instead of a six-pulse diode bridge of each converter cell, has a self-commutated pulse converter. Such a self-commutated pulse converter on the supply side is also referred to as an Active Front End (AFE). The use of an AFE for each converter cell of this three-phase cell converter now enables power to be fed back into a network. In addition this AFE can be controlled such that the power factor is cos=1 and that the intermediate circuit voltage of each converter cell can be regulated to a predetermined constant amount. A converter cell as a constructional unit is shown in FIG. 5 of this EP patent. FIG. 6 of this EP patent shows a support structure for accepting a number of converter cells. This support structure comprises a number of support rails, a backplane circuit board, two guide rails for a converter cell in each case and two side walls. The backplane circuit board has terminals for each converter cell. The guide rails for the converter cells are disposed at three levels on the support rails, which mechanically connect the two side walls of this support structure to one another. This support structure is embodied for a three-phase cell converter with three converter cells per phase in each case Whether these converter cells of one phase are disposed in one level alongside one another or over three levels above one another, cannot be ascertained from this EP patent.
If a cell converter with a higher output voltage is needed, which lies in terms of amplitude above the value of the output voltage of the cell converter of the Siemens brochure, at least one further converter cell per phase must be provided. In order to be able to manufacture such a cell converter with five converter cells per phase in each case, the valve cabinet must be expanded by one converter cell width. At the same time the converter transformer must be provided with a further three-phase secondary winding system. These three further converter cells must each be connected to a further three-phase secondary winding system of the converter transformer electrically-conductively on the supply side and electrically connected in series with the four converter cells of a phase already present on the output side.
The Siemens brochure “Der wassergekühlte Mittelspannungsumrichter der Wahl” (The water-cooled medium-voltage converter of choice) with the order number E20001-A40-P590, published in July 2009, discloses how the overall weight of a intermediate voltage circuit converter with load-side cell converter increases as the level of the converter output voltage increases, wherein the change depends on the expansion in width of the valve cabinet. In accordance with the two said brochures the converter family “ROBICON Perfect Harmony” has a converter with a number of cabinets for different output voltages in each case. This converter family cannot be adapted individually to any given output voltages.